The present invention relates to an improved method and apparatus for making a necked container and to the necked container formed thereby. More particularly, the invention relates to an improved method and apparatus for making a necked container wherein one end of the container is necked-in at least 15% from the original container diameter so as to be useful as an aerosol can, for example.
In the past there have generally been two basic kinds of necked aerosol containers: those made of steel sheet material such as tin plate, and those made of aluminum. In the case of steel sheet material, one form of construction for the aerosol containers has been the three-piece container having a cylindrical container body with a longitudinally extending soldered or welded lap joint and with a dome-shaped top and a bottom seamed thereon. Steel sheet material aerosol containers have also been formed out of flat steel sheet by a method called drawn and ironed. On such cans a dome-shaped top is mounted to form a two-piece container. Another drawn and ironed technique involves forming a steel cup, cutting a hole in the cup and curling the adjacent edge to form a necked top and then seaming a bottom to the cup.
Necked aerosol containers of aluminum may be made by a method which involves forming so-called monoblocs from an aluminum slug into a cup. The top of the cup is formed with a relatively small opening and an outside curl on which an aerosol valve is mounted. A drawn and ironed process may also be used to form aluminum aerosol containers from flat sheets of aluminum. A two-piece aluminum can formed by such a method has a dome-shaped top which is mounted the same way as on a tinplate three-piece container. Aluminum aerosol containers may also be integrally formed with a top having a relatively small opening for an aerosol valve and with the bottom of the container being seamed on to form a two-piece container.
Thus, it is known to make necked aerosol containers either by providing a cylindrical container body with a special end or by shaping the end of a container particularly when the container is formed of readily workable metal, such as aluminum. However, until recently the forming of a dome from a steel can body has been impractical from a commercial standpoint.
It is known to reduce the diameter of an end portion of a can body by a series of necking-in operations. However, in such bodies in lieu of the conventional smooth dome appearance there has generally been either a series of steps or a very wrinkled appearance.
U.S. Pat. No. 4,261,193 discloses a method and apparatus for making a necked steel aerosol container having an integral dome wherein the container is formed by welding the overlapping longitudinally extending edges of a steel sheet which has been formed into a cylindrical can body and thereafter progressively necking-in the welded can body. In this known process tbe overlapped edges of the cylindrical container body are welded together by a conventional welding process such as electrical resistance welding. With such a welded cylindrical can body the wall thickness of the can body is greater at the welded side seam than it is elsewhere about the circumference of the can body. Thus, necking of this known type of cylindrical container body is problematical in that it is not commercially feasible to orient the lap weld side seam with the tooling during the necking operations and therefore in the apparatus disclosed in the aforesaid patent, it is necessary that the outside tools be permitted to float radially in order to maintain the required clearance at all circumferential points between the tools of each set of tooling. The greater thickness of the lap weld side seam may also adversely affect the appearance of the necked container in that the uneven or discontinuous nature of the weld and subsequent wrinkles from forming may be readily visible by the casual observer. The method and apparatus for making a necked container disclosed in the aforesaid patent are also disadvantageous in that they require a complete assembly and disassembly of the lap welded can body with respect to each of a plurality of sets of necking tools. Thus, either the can body or entire sets of tools must be transferred from station-to-station during the necking-in steps which can be a relatively slow process subject to damaging either the cans or the tools.
An object of the present invention is to provide an improved method and apparatus for making a necked aerosol container for an aerosol can, for example, which avoid the aforementioned disadvantages of the prior art. More particularly, an object of the invention is to provide an improved method and apparatus for making a necked container which may be formed from welded sheet material thereby providing a container which is relatively low in cost as compared with the prior containers such as the aluminum monobloc container.
A further object of the invention is to provide an improved method and apparatus for making a necked container having an integral dome wherein the container is formed from a cylindrical can body having a longitudinal side seam and wherein the dome is formed by a progressive necking-in process such that the dome-shaped configuration is smooth instead of being provided with a series of steps or a wrinkled appearance.
An additional object of the present invention is to provide an improved method and apparatus for making a necked container such that it is possible to progressively neck-in the end of a welded steel cylindrical can body without getting a wrinkle or an S-curve during necking and without necessitating the use of sets of tooling that float radially and that must be completely exchanged with each successive necking-in step.
These and other objects of the present invention are attained by providing a method of making a necked tubular member comprising the steps of forming a sheet of material into a generally cylindrical tubular member and butt welding the adjacent longitudinal extending edges of the sbeet, arranging the butt welded tubular member about a mandrel having a free end portion with a dome-shaped surface, reducing the diameter of a free end portion of the tubular member and forming an intermediate portion between the the reduced diameter free end portion and the remainder of the tubular member whioh extends along a portion of the dome-shaped surface of the mandrel, and further reducing the diameter of the free end portion of the tubular member and increasing the extent of the intermediate portion along the dome-shaped surface of the mandrel.
The step of further reducing the diameter of the free end portion of the tubular member and increasing the extent of the intermediate portion along the dome-shaped surface of the mandrel is repeated until the diameter of the free end is reduced at least approximately 15% from the original diameter of the tubular member and, according to a disclosed embodiment, until the diameter of the free end is on the order of one-half of the original diameter. The diameter of the free end portion of the tubular member is reduced approximately 7 to 8% in each of the initial reducing steps and 3 to 4% in the final steps to reach a final diameter which is on the order of one-half of the original diameter.
The method of the invention includes the additional step of trimming the reduced free end portion of the tubular member and curling it. In one form of the invention the free end portion of the tubular member is curled by first beading the free end portion inwardly and then curling it inwardly on itself so that the trimmed edge thereof is tucked inside the curl.
An apparatus of the invention for progressively necking-in an end portion of the butt welded tubular member comprises a first inside tool of a first diameter, a free end portion of said inside tool having a dome-shaped surface, a plurality of second inside tools each having a second diameter which is less than the first diameter of the first inside tool and having a free end portion for positioning adjacent the dome-shaped surface of the first inside tool with the dome-shaped surface extending between the first diameter of the first inside tool and the second diameter of the second inside tool, the second diameter of the second inside tools progressively decreasing so that the extent of the dome-shaped surface between the first and second diameter progressively increases, and a plurality of outside tools cooperable with the first inside tool and respective ones of the second inside tools.
In a disclosed embodiment of the apparatus, each of the plurality of outside tools have an internal configuration with a first portion cooperable with the first diameter of the first inside tool, a second portion cooperable with the dome-shaped surface extending between the first diameter of the first inside tool and second diameters of one of the second inside tools and a third portion cooperable with the second diameter of one of the second inside tools. In the disclosed embodiment, the second diameter of the second inside tools progressively decreases to a diameter on the order of one-half of the first diameter.
Means are provided for moving one of the first inside tool and a cooperable pair of a second inside tool and an outside tool with respect to the other for effecting necking-in of the end portion of the tubular member. In the illustrated embodiment, the means for moving comprises a press ram which moves the cooperable pair with respect to the first inside tool in a direction along the longitudinal axis of a tubular member to be necked-in which is located about the first inside tool.
According to a further feature of the invention, means are provided for mounting the second inside tool of the cooperable pair in a leading and relatively movable position with respect to the outside tool so that with relative movement of the cooperable pair with respect to the first inside tool, the second inside tool reaches a position adjacent the dome-shaped surface of the first inside tool while the outside tool continues to move with respect to both the first and second inside tools for effecting necking-in of the end portion of the tubular member. The means for mounting the second inside tool of the cooperable pair in a leading and relatively movable position with respect to the outside tool includes a spring for yieldably biasing the second inside tool in the leading position.
As an additional feature of the invention, the second inside tool of the cooperable pair includes an abutment member located centrally in its free end portion for contacting a portion of the first inside tool when the second inside tool is positioned adjacent the dome-shaped surface. A recess is provided in the center of the free end portion of the first inside tool for receiving the abutment member when the second inside tool is positioned adjacent the dome-shaped surface. A spacer is located in the recess for contacting the abutment member to control the relative positions of the first and second inside tools.
With the method and apparatus of the invention, it is possible to progressively neck-in a free end portion of the butt welded tubular member to form a dome-shaped surface without the use of outside tools which float radially and without getting wrinkles or an S-curve during necking-in. This necking-in process is facilitated by the fact that the thickness of the butt weld in the can body is the same or essentially the same as the wall thickness of the can body outside the weld area, and by the relatively small weld heat-affected zone and minimal degradation of base material properties associated therewith which result from welding with a high energy density welding process such as laser welding or electron beam welding wherein the energy density is at least 10.sup.6 per square inch.
The necked container body of the invention comprises a welded tubular member having a butt welded joint extending longitudinally thereof, one end of the welded tubular member being necked-in to a diameter which is reduced by at least approximately 15% from the original diameter of the tubular member with the necked-in end of the tubular member having a dome-shaped configuration. In the disclosed embodiment one end of the tubular member is necked-in to a diameter which is reduced on the order of one-half of the original diameter of the tubular member and the free end of the necked end is curled inwardly on itself with the edge of the free end being tucked inside the curl.
These and other objects, features and advantages of the present invention will become more apparent from the following description when taken in connection with the accompanying drawings which show, for purposes of illustration only, several embodiments in accordance with the invention.